The objective is to isolate chemical agents from a peripheral receptor in the skin which will attract or nourish sensory nerves. This may be of benefit to individuals who have suffered sensory loss due to nerve trauma or burn wounds. The specific aims are to determine if; 1) special cells in the epidermis, called Merkel cells, attract sensory nerves to the skin; 2) the number of Merkel cell receptors a nerve can support is fixed or determined by receptor availability; and 3) the regeneration of these receptors in adult animals differs from their fetal development. To test whether Merkel cells attract sensory neurons, Merkel cell rich epidermis will be cultured in vitro in the presence of dorsal root sensory ganglia. The outgrowth of neurites from the ganglia will be compared with that of ganglia cultured alone or in the presence of simple epidermis devoid of receptor cells. This will also be tested in vivo by transplanting Merkel cell receptors, called touch domes, into denervated regions of skin and seeing if nerves will be induced to reinnervate the skin. Skin will be examined by silver stains for nerves, electron microscopy and nerve recordings. Whether the number of touch dome receptors a sensory nerve can innervate is fixed will be examined by manipulating the number of domes normally present in a cutaneous nerve field by excising and transplanting them. After making experimental changes in dome patterns, the sensory nerve will be crushed. One month after the nerve has regenerated, it will be recorded from again to determine the number of receptors it now innervates. Sites where domes were excised from will be examined by electron microscopy and nerve recordings to monitor the processes of dome receptor regeneration.